Method of Making a Laminated Glass/Polyolefin Film Structure

ABSTRACT

Laminated structures comprising a (i) glass layer, (ii) first alkoxysilane-containing polyolefin (PO) layer, (iii) catalyst layer, and (iv) second alkoxysilane-containing polyolefin layer, each layer having opposing facial surfaces, are prepared by a method comprising the steps of applying in adhering contact: A. One facial surface of the first PO layer to one facial surface of the glass layer; B. The catalyst layer to the facial surface of the first PO layer opposite the facial surface of the first PO layer in adhering contact with the glass layer; and C. The second PO layer to the facial surface of the catalyst layer opposite the facial surface of the catalyst layer in adhering contact with the first PO layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. patent application Ser.No. 61/080,849, filed on Jul. 15, 2008, the entire content of which isincorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to laminated structures. In one aspect, theinvention relates to laminated structures of glass and polyolefin filmwhile in another aspect, the invention relates to photovoltaic modules.In still another aspect, the invention relates to a method of making alaminated structure in which a polyolefin film is in adhering contactwith glass while in yet another aspect, the invention relates to amethod making a laminated structure in which the polyolefin film is bothsilane-crosslinked and exhibits good adhesion to glass.

BACKGROUND OF THE INVENTION

The most common incumbent material for an encapsulant in a photovoltaic(PV) panel is poly(ethylene-co-vinyl acetate) (EVA). Optical clarity,moldability and low cost are among its desirable qualities. During thelamination process to construct a typical PV panel, the EVA encapsulantis chemically crosslinked by the action of an organic peroxide. Theprimary disadvantage of EVA as an encapsulant is that it is susceptibleto hydrolysis by reaction with ambient moisture, which results in theformation of acetic acid which in turn can damage the PV cell. As aconsequence, PV panels made with EVA have an unacceptably short life.

Low density polyolefins, such as poly(ethylene-co-octene) satisfy manyof the requirements of an encapsulant, including optical clarity,moldability and low cost (even lower than EVA), plus they are notaffected by hydrolysis. However, unmodified polyolefins do not havesufficient adhesion to glass, nor do they have sufficient mechanicalstrength at elevated temperatures.

Polyolefins that are modified to contain trialkoxysilane functionalgroups exhibit acceptable adhesion to glass because during thelamination process to construct the PV panel, the alkoxysilane groups inthe resin and the silanol groups that naturally occur at the surface ofthe glass undergo a non-catalyzed condensation reaction that form strongand hydrolytically stable siloxane linkages between the resin and theglass. However, such an encapsulant still does not have sufficientmechanical strength at elevated temperatures.

Polyolefins that contain trialkoxysilane groups will react with water inthe presence of a catalyst to form silanol functional groups, and thesegroups further react with each other, also in the presence of acatalyst, to form siloxane crosslinks. Typically, these two reactionsoccur very slowly in the absence of a catalyst. Catalysts for thesereactions can be either an acid or base. Lewis acids are commonly usedto induce crosslinking. The crosslinked encapsulant has very goodmechanical strength at elevated temperatures, but it exhibits pooradhesion to glass. This is because some of the alkoxysilane groups onthe surface of the encapsulant that are required for reaction with theglass surface have been converted to siloxane groups, and siloxanegroups are not reactive with the glass surface. Thus the morealkoxysilane groups on the surface of the encapsulant that have beenconverted to siloxane groups, the poorer the adhesion of the encapsulantto the glass surface.

For these and other reasons, the industry for laminated glass/polyolefinfilm laminated structures, such as PV panels, has a continuing interestin developing a method for preparing a structure in which thepolyolefin-containing alkoxysilane groups is both crosslinked andexhibits good adhesion to the glass.

BRIEF SUMMARY OF THE INVENTION

According to this invention, the polymeric film or encapsulant is apolyolefin that contains alkoxysilane groups, and during the laminationprocess to construct the a laminated structure of polyolefin film andglass, e.g., a PV panel, a catalyst for promoting the crosslinking ofthe alkoxysilane groups is applied in a controlled fashion such that thecrosslinking process can proceed within the bulk of the resin, and theprocess of adhering the polyolefin film to the glass can proceed at thesurface of the resin. Adding the crosslinking catalyst to the extruderas the film is cast results in a homogeneous distribution of catalystthroughout the film and this, in turn, results in a film that does nothave good adhesion to glass. However, by adding the catalyst away fromthe surface of the film that will contact the glass, both good adhesionand good mechanical strength at elevated temperature are obtained.

In one embodiment, the invention is a laminated structure comprising (i)a first layer having opposing first and second facial surfaces andcomprising an alkoxysilane-containing polyolefin (PO), and (ii) a secondlayer having opposing first and second facial surfaces and comprising acatalyst to promote the crosslinking of the alkoxysilane-containing POof the first layer, one facial surface of the first layer in adheringcontact with one facial surface of the second layer.

In one embodiment, the invention is a method of making a laminatedstructure, the structure comprising (i) a glass layer, (ii) a firstalkoxysilane-containing PO layer, (iii) a catalyst layer, and (iv) asecond alkoxysilane-containing polyolefin layer, each layer havingopposing facial surfaces, the method comprising the steps of applying inadhering contact:

-   -   A. One facial surface of the first PO layer to one facial        surface of the glass layer;    -   B. The catalyst layer to the facial surface of the first PO        layer opposite the facial surface of the first PO layer in        adhering contact with the glass layer; and    -   C. The second PO layer to the facial surface of the catalyst        layer opposite the facial surface of the catalyst layer in        adhering contact with the first PO layer.        The layers can be applied to one another in any order, e.g., the        second PO layer can be applied to the catalyst layer before the        catalyst layer is applied to the first PO layer, or the catalyst        layer can be applied to the first PO layer before the first PO        layer is applied to the glass.

In one embodiment, the catalyst may be painted, sprayed, or wiped on thesurface of the first PO layer that is opposite the facial surface of thePO layer that is to contact with the glass. The catalyst may be appliedas a pure substance, or it may be dissolved in a solvent, dispersed inan inert carrier, or emulsified.

In one embodiment, the catalyst may be homogeneously distributed withina thin film comprising a polyolefin that has not been modified withalkoxysilane functional groups. This film is applied as one layer of amulti-layer laminate structure. Thus, in the lamination process toconstruct, for example, a PV panel, the first PO layer is applied to theglass, and then a thin film containing the catalyst is placed in contactwith the first PO layer forming a sandwich structure with the glass onone side, the film with catalyst on the other side, and the first POlayer in the center. The catalyst can diffuse from the thin film intothe first PO layer to catalyze crosslinking. The film containing thecatalyst is not crosslinked, and it can be prepared by adding thecatalyst to a polymer melt. The film is extruded sufficiently thin suchthat it will not deleteriously affect the mechanical strength of thelaminated structure at an elevated temperature.

In one embodiment, the invention is the laminated structure made by themethod described above. The laminated structure can take the form of,among other things, a PV-panel or module, or a solar cell, or safetyglass, or insulating glass or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a five-layer laminate structure of whichthe fourth layer is a catalyst layer.

FIG. 2 illustrates a scheme of architecture for compression molding.

FIG. 3 is a graph reporting the effect of catalyst concentration on theadhesion of a PO film layer to glass.

FIG. 4 is a graph reporting comparative DMTA results of a crosslinked POand EVA as a function of temperature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The numerical ranges in this disclosure are approximate, and thus mayinclude values outside of the range unless otherwise indicated.Numerical ranges include all values from and including the lower and theupper values, in increments of one unit, provided that there is aseparation of at least two units between any lower value and any highervalue. As an example, if a compositional, physical or other property orprocess parameter, such as, for example, molecular weight, viscosity,melt index, temperature, etc., is from 100 to 1,000, it is intended thatall individual values, such as 100, 101, 102, etc., and sub ranges, suchas 100 to 144, 155 to 170, 197 to 200, etc., are expressly enumerated.For ranges containing values which are less than one or containingfractional numbers greater than one (e.g., 1.1, 1.5, etc.), one unit isconsidered to be 0.0001, 0.001, 0.01 or 0.1, as appropriate. For rangescontaining single digit numbers less than ten (e.g., 1 to 5), one unitis typically considered to be 0.1. These are only examples of what isspecifically intended, and all possible combinations of numerical valuesbetween the lowest value and the highest value enumerated, are to beconsidered to be expressly stated in this disclosure. Numerical rangesare provided within this disclosure for, among other things, density,melt index, amount of alkoxysilane groups in the PO resin, and relativeamounts of ingredients in various formulations

The term “comprising” and its derivatives are not intended to excludethe presence of any additional component, step or procedure, whether ornot the same is specifically disclosed. In order to avoid any doubt, anyprocess or composition claimed through use of the term “comprising” mayinclude any additional steps, equipment, additive, adjuvant, or compoundwhether polymeric or otherwise, unless stated to the contrary. Incontrast, the term, “consisting essentially of” excludes from the scopeof any succeeding recitation any other component, step or procedure,excepting those that are not essential to operability. The term“consisting of” excludes any component, step or procedure notspecifically delineated or listed. The term “or”, unless statedotherwise, refers to the listed members individually as well as in anycombination.

“Composition” and like terms mean a mixture of two or more materials.Included in compositions are pre-reaction, reaction and post-reactionmixtures the latter of which will include reaction products andby-products as well as unreacted components of the reaction mixture anddecomposition products, if any, formed from the one or more componentsof the pre-reaction or reaction mixture.

“Blend”, “polymer blend” and like terms mean a composition of two ormore polymers. Such a blend may or may not be miscible. Such a blend mayor may not be phase separated. Such a blend may or may not contain oneor more domain configurations, as determined from transmission electronspectroscopy, light scattering, x-ray scattering, and any other methodknown in the art. Blends are not laminates, but one or more layers of alaminate may contain a blend.

“Polymer” means a polymeric compound prepared by polymerizing monomers,whether of the same or a different type. The generic term polymer thusembraces the term homopolymer, usually employed to refer to polymersprepared from only one type of monomer, and the term interpolymer asdefined below. It also embraces all forms of interpolymers, e.g.,random, block, etc. The terms “ethylene/α-olefin polymer”,“propylene/α-olefin polymer” and “silane copolymer” are indicative ofinterpolymers as described below.

“Interpolymer” means a polymer prepared by the polymerization of atleast two different monomers. This generic term includes copolymers,usually employed to refer to polymers prepared from two differentmonomers, and polymers prepared from more than two different monomers,e.g., terpolymers, tetrapolymers, etc.

“Catalytic amount” and like terms means an amount of catalyst sufficientto promote the rate of reaction between two or more reactants by adiscernable degree.

“Crosslinking amount” and like terms means an amount of crosslinkingagent or radiation or moisture or any other crosslinking compound orenergy sufficient to impart at least a detectable amount of crosslinkingin the composition or blend under crosslinking conditions.

“Layer” means a single thickness, coating or stratum continuously ordiscontinuously spread out or covering a surface.

“Multi-layer” means at least two layers.

“Facial surface”, “planar surface” and like terms mean the surfaces ofthe layers that are in contact with the opposite and adjacent surfacesof the adjoining layers. Facial surfaces are in distinction to edgesurfaces. A rectangular layer comprises two facial surfaces and fouredge surfaces. A circular layer comprises two facial surfaces and onecontinuous edge surface.

“In adhering contact” and like terms mean that one facial surface of onelayer and one facial surface of another layer are in touching andbinding contact to one another such that one layer cannot be removed forthe other layer without damage to the in-contact facial surfaces of bothlayers.

Polyolefin Resins

The polyolefin copolymers useful in the practice of this inventiontypically have, before grafting, a density of less than 0.91, preferablyless than 0.905, more preferably less than 0.89, even more preferablyless than 0.88 and even more preferably less than 0.875, grams per cubiccentimeter (g/cm³). The polyolefin copolymers typically have a densitygreater than 0.85, preferably greater than 0.855 and more preferablygreater than 0.86, g/cm³. Density is measured by the procedure of ASTMD-792. Low density polyolefin copolymers are generally characterized assemi-crystalline, flexible and having good optical properties, e.g.,high transmission of visible and UV-light and low haze.

The polyolefin copolymers useful in the practice of this inventiontypically have, before grafting, a melt index greater than 0.10 andpreferably greater than 1 gram per 10 minutes (g/10 min). The polyolefincopolymers typically have a melt index of less than 75 and preferably ofless than 10, g/10 min. Melt index is measured by the procedure of ASTMD-1238 (190° C./2.16 kg).

The polyolefin copolymers useful in the practice of this invention andthat are made with a single site catalyst such as a metallocene catalystor constrained geometry catalyst, typically have, before grafting, amelting point of less than about 95, preferably less than about 90, morepreferably less than about 85, even more preferably less than about 80and still more preferably less than about 75, C. For polyolefincopolymers made with multi-site catalysts, e.g., Ziegler-Natta andPhillips catalysts, the melting point is typically 125 to 127 C. Themelting point is measured by differential scanning calorimetry (DSC) asdescribed, for example, in U.S. Pat. No. 5,783,638. Polyolefincopolymers with a low melting point often exhibit desirable flexibilityand thermoplasticity properties useful in the fabrication of the modulesof this invention.

The polyolefin copolymers useful in the practice of this inventioninclude ethylene/alpha-olefin interpolymers having a α-olefin content ofbetween about 15, preferably at least about 20 and even more preferablyat least about 25, weight percent (wt %) based on the weight of theinterpolymer. These interpolymers typically have an α-olefin content ofless than about 50, preferably less than about 45, more preferably lessthan about 40 and even more preferably less than about 35, wt % based onthe weight of the interpolymer. The α-olefin content is measured by ¹³Cnuclear magnetic resonance (NMR) spectroscopy using the proceduredescribed in Randall (Rev. Macromol. Chem. Phys., C29 (2&3)). Generally,the greater the α-olefin contents of the interpolymer, the lower thedensity and the more amorphous the interpolymer.

The α-olefin is preferably a C₃₋₂₀ linear, branched or cyclic α-olefin.Examples of C₃₋₂₀ α-olefins include propene, 1-butene,4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene,1-tetradecene, 1-hexadecene, and 1-octadecene. The α-olefins can alsocontain a cyclic structure such as cyclohexane or cyclopentane,resulting in an α-olefin such as 3-cyclohexyl-1-propene (allylcyclohexane) and vinyl cyclohexane. Although not α-olefins in theclassical sense of the term, for purposes of this invention certaincyclic olefins, such as norbornene and related olefins, are α-olefinsand can be used in place of some or all of the α-olefins describedabove. Similarly, styrene and its related olefins (for example,α-methylstyrene, etc.) are α-olefins for purposes of this invention.Acrylic and methacrylic acid and their respective ionomers, andacrylates and methacrylates, however, are not α-olefins for purposes ofthis invention. Illustrative polyolefin copolymers includeethylene/propylene, ethylene/butene, ethylene/1-hexene,ethylene/1-octene, ethylene/styrene, and the like. Ethylene/acrylic acid(EAA), ethylene/methacrylic acid (EMA), ethylene/acrylate ormethacrylate, ethylene/vinyl acetate and the like are not polyolefincopolymers of this invention. Illustrative terpolymers includeethylene/propylene/1-octene, ethylene/propylene/butene,ethylene/butene/1-octene, and ethylene/butene/styrene. The copolymerscan be random or blocky.

More specific examples of olefinic interpolymers useful in thisinvention include very low density polyethylene (VLDPE) (e.g., FLEXOMER®ethylene/1-hexene polyethylene made by The Dow Chemical Company),homogeneously branched, linear ethylene/α-olefin copolymers (e.g.TAFMER® by Mitsui Petrochemicals Company Limited and EXACT® by ExxonChemical Company), homogeneously branched, substantially linearethylene/α-olefin polymers (e.g., AFFINITY® and ENGAGE® polyethyleneavailable from The Dow Chemical Company), and olefin block copolymerssuch as those described in U.S. Pat. No. 7,355,089 (e.g., INFUSE®available from The Dow Chemical Company). The more preferred polyolefincopolymers are the homogeneously branched linear and substantiallylinear ethylene copolymers. The substantially linear ethylene copolymersare especially preferred, and are more fully described in U.S. Pat. Nos.5,272,236, 5,278,272 and 5,986,028.

The polyolefin copolymers useful in the practice of this invention alsoinclude propylene, butene and other alkene-based copolymers, e.g.,copolymers comprising a majority of units derived from propylene and aminority of units derived from another α-olefin (including ethylene).Exemplary propylene polymers useful in the practice of this inventioninclude the VERSIFY® polymers available from The Dow Chemical Company,and the VISTAMAXX® polymers available from ExxonMobil Chemical Company.

Blends of any of the above olefinic interpolymers can also be used inthis invention, and the polyolefin copolymers can be blended or dilutedwith one or more other polymers to the extent that the polymers are (i)miscible with one another, (ii) the other polymers have little, if any,impact on the desirable properties of the polyolefin copolymer, e.g.,optics and low modulus, and (iii) the polyolefin copolymers of thisinvention constitute at least about 70, preferably at least about 75 andmore preferably at least about 80, weight percent of the blend.

The PO resins used in the first and second alkoxysilane-containing POlayers of the laminated structure of this invention contain, of course,alkoxysilane groups. Typically, the alkoxysilane groups are grafted to aPO resin. Any silane that will effectively graft to and crosslink thepolyolefin copolymer and lead to adhesion to glass can be used in thepractice of this invention. Suitable silanes include unsaturated silanesthat comprise an ethylenically unsaturated hydrocarbyl group, such as avinyl, allyl, isopropenyl, butenyl, cyclohexenyl or γ-(meth)acryloxyallyl group, and a hydrolyzable group, such as, for example, ahydrocarbyloxy, hydrocarbonyloxy, or hydrocarbylamino group. Examples ofhydrolyzable groups include methoxy, ethoxy, formyloxy, acetoxy,proprionyloxy, and alkyl or arylamino groups. Preferred silanes are theunsaturated alkoxy silanes which can be grafted onto the polymer. Thesesilanes and their method of preparation are more fully described in U.S.Pat. No. 5,266,627. Vinyl trimethoxy silane, vinyl triethoxy silane,γ-(meth)acryloxy propyl trimethoxy silane and mixtures of these silanesare the preferred silane crosslinkers for is use in this invention.

Alternatively, silane copolymers, e.g., SILINK™poly(ethylene-co-vinyltrimethoxysilane) copolymer, can be used in placeof or in combination with ethylene polymers grafted or otherwisemodified with alkoxysilane groups.

The amount of silane crosslinker used in the practice of this invention,either as a group grafted to a polyolefin backbone or as unitincorporated into the polymer chain as in a silane copolymer, can varywidely depending upon the nature of the polyolefin or silane copolymer,the silane, the processing conditions, the grafting efficiency, theultimate application, and similar factors, but typically at least 0.2,preferably at least 0.5, wt % is used based on the weight of thecopolymer. Considerations of convenience and economy are usually the twoprincipal limitations on the maximum amount of silane crosslinker usedin the practice of this invention, and typically the maximum amount ofsilane crosslinker does not exceed 5, preferably it does not exceed 3,wt % based on the weight of the copolymer.

In those embodiments comprising two or more layers ofalkoxysilane-containing PO, the amount of alkoxysilane in each layer canbe the same or different, and each layer can contain the same ordifferent alkoxysilane, e.g., in one layer the PO can be grafted withvinyl trimethoxy silane while the other layer the same or different POis grafted with vinyl ethoxy silane, or in one layer the PO is graftedwith vinyl methoxy silane while the other layer comprisespoly(ethylene-co-vinyltrimethoxysilane) copolymer. In one embodiment,the amount of alkoxysilane in one layer is at least twice, thrice orfour-times as much as the alkoxysilane in the other layer, or at leastone of the other layers.

The silane crosslinker is grafted to the PO polymer by any conventionalmethod, typically in the presence of a free radical initiator e.g.peroxides and azo compounds, or by ionizing radiation, etc. Organicinitiators are preferred, such as any one of the peroxide initiators,for example, dicumyl peroxide, di-tert-butyl peroxide, t-butylperbenzoate, benzoyl peroxide, cumene hydroperoxide, t-butyl peroctoate,methyl ethyl ketone peroxide, 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane,lauryl peroxide, and tert-butyl peracetate. A suitable azo compound isazobisisobutyl nitrile. The amount of initiator can vary, but it istypically present in an amount of at least 0.02, preferably at least0.03, phr. Typically, the initiator does not exceed 0.15, preferably itdoes not exceed about 0.10, phr. The ratio of silane crosslinker toinitiator also can vary widely, but the typical crosslinker:initiatorratio is between 10:1 to 150:1, preferably between 18:1 and 100:1.

While any conventional method can be used to graft the silanecrosslinker to the PO polymer, one preferred method is blending the twowith the initiator in the first stage of a reactor extruder, such as aBuss kneader. The grafting conditions can vary, but the melttemperatures are typically between 160 and 260° C., preferably between190 and 230° C., depending upon the residence time and the half life ofthe initiator.

The polymeric materials of this invention can comprise additives otherthan or in addition to cure promoters. For example, such other additivesinclude UV-stabilizers and processing stabilizers such as trivalentphosphorus compounds. The UV-stabilizers are useful in lowering thewavelength of electromagnetic radiation (e.g., to less than 360 nm),that can be absorbed by a laminated structure, e.g., a PV module, andinclude hindered phenols such as Cyasorb UV2908 and hindered amines suchas Cyasorb UV 3529, Hostavin N30, Univil 4050, Univin 5050, ChimassorbUV 119, Chimassorb 944 LD, Tinuvin 622 LD and the like. The phosphoruscompounds include phosphonites (PEPQ) and phosphites (Weston 399, TNPP,P-168 and Doverphos 9228). The amount of UV-stabilizer is typically fromabout 0.1 to 0.8%, and preferably from about 0.2 to 0.5%. The amount ofprocessing stabilizer is typically from about 0.02 to 0.5%, andpreferably from about 0.05 to 0.15%.

Still other additives include, but are not limited to, antioxidants(e.g., hindered phenolics such as Irganox® 1010 made by Ciba GeigyCorp.), cling additives (e.g., polyisobutylene), anti-blocks,anti-slips, pigments and fillers (clear if transparency is important tothe application). In-process additives, e.g. calcium stearate, water,etc., may also be used. These and other potential additives are used inthe manner and amount as is commonly known in the art.

Glass

Glass in the common sense refers to a hard, brittle, transparent solid,such as that used for windows, many bottles, or eyewear, including, butnot limited to, soda-lime glass, borosilicate glass, acrylic glass,sugar glass, isinglass (Muscovy-glass), or aluminum oxynitride. In thetechnical sense, glass is an inorganic product of fusion which has beencooled to a rigid condition without crystallizing. Many glasses containsilica as their main component and glass former.

Pure silicon dioxide (SiO₂) glass (the same chemical compound as quartz,or, in its polycrystalline form, sand) does not absorb UV light and isused for applications that require transparency in this region. Largenatural single crystals of quartz are pure silicon dioxide, and uponcrushing are used for high quality specialty glasses. Syntheticamorphous silica, an almost 100% pure form of quartz, is the rawmaterial for the most expensive specialty glasses.

The glass layer of the laminated structure is typically one of, withoutlimitation, window glass, plate glass, silicate glass, sheet glass,float glass, colored glass, specialty glass which may, for example,include ingredients to control solar heating, glass coated withsputtered metals such as silver, glass coated with antimony tin oxideand/or indium tin oxide, E-glass, SOLEX™ glass (available from PPGIndustries of Pittsburgh, Pa.) and TOROGLASS™. Alternatively, the glasslayer, which may be a rigid or flexible sheet comprising apolycarbonate, an acrylic, a polyacrylate, a cyclic polyolefin such asethylene norbornene, metallocene-catalyzed polystyrene and mixtures oftwo or more of these materials.

Catalyst

Cure is promoted with a crosslinking catalyst, and any catalyst thatwill provide this function can be used in the practice of thisinvention. The catalyst used in the practice of this invention is aLewis or Bronsted acid or base that is of sufficient strength tocatalyze the crosslinking reaction at a concentration of less than 1 wt%, preferably less than about 5000 parts per million (ppm) and morepreferably less than 2500 ppm, and as low as 100 ppm. The catalyst isresistant to decomposition under the conditions used to construct thelaminated structure. Preferably, the catalyst will diffuse sufficientlyrapidly through the PO resin during and after the lamination process tocontact the alkoxysilane groups. Preferably, the catalyst will notinterfere with or deteriorate the performance of the laminatedstructure, e.g., a photovoltaic cell, during the useful life of thestructure. The catalyst preferably does not interfere with ordeteriorate the adhesion of the PO resin to glass. Many materials canact as catalysts that are known to those familiar with the art,including, without limitation, aromatic sulfonic acids, organic tincompounds, organic titanium compounds, organic zinc compounds, andorganic zirconium compounds. Specific examples includedodecylbenzenesulfonic acid, dibutyltin dilaurate andneopentyl(diallyloxy)zirconium trineodecanoate, produced commerciallyunder the trade name Ken-React NZ01 by Kenrich Petrochemicals.

In one embodiment, the catalyst may be painted, sprayed, wiped orotherwise applied to the surface of the first PO layer that is oppositefrom the surface of the first PO layer that is in contact with the glasslayer. The catalyst may be applied as a pure substance, or it mayoptionally be dissolved in a solvent, dispersed in an inert carrier, oremulsified. After the catalyst is applied to the glass layer and thusforming a catalyst layer over the first PO layer, the second PO layer isapplied to the surface of the catalyst layer that is opposite thesurface of the catalyst layer that is in contact with the first POlayer. The resulting laminate is a multi-layer structure comprisinglayers of glass, a first silane-containing PO film, catalyst, and asecond silane-containing PO film. In this structure, the catalyst candiffuse throughout the film layers to catalyze crosslinking with little,if any, interference with the reaction between the silane groups of thefirst PO layer and those of the glass layer.

In another embodiment, the catalyst may be homogeneously distributed ina thin film made up of a polyolefin that has not been modified withalkoxysilane functional groups, and this film is applied as one layer ofa multi-layer laminate structure. In a preferred variant of thisembodiment, the polyolefin of the film that contains the catalyst is thesame polyolefin that is modified with alkoxysilane groups that forms thefirst and second PO layers of the laminate structure. Thus, in thelamination process to construct the laminated structure, the polyolefinthat contains alkoxysilane groups is placed in contact with the glass,and the thin film containing the catalyst is placed in contact with thesilane-containing film, forming a sandwich structure with the glass onone side, the film with catalyst on the other side, and thesilane-containing film in the center. The catalyst can diffuse from thethin film into the silane-containing film to catalyze crosslinking. Thefilm containing the catalyst can be prepared by adding the catalyst tothe polymer melt in an extruder. Because this particular film layer isnot crosslinked, the film is prepared sufficiently thin, e.g., between0.1 and 2, preferably between 0.2 and 2 and more preferably between 0.3and 0.5, millimeters (mm), such that it will not deleteriously affectthe mechanical strength of the structure at elevated temperatures.

The alkoxysilane-containing polyolefin copolymers after crosslinkinghave a gel content, as measured by ASTM D-2765, of at least 40,preferably at least 50 and more preferably at least 60 and even morepreferably at least 70, percent. Typically, the gel content does notexceed 90 percent.

Laminated Structure

The laminated structures of this invention are structures comprising (i)a glass layer, (ii) a first alkoxysilane-containing polyolefin (PO)layer, (iii) a catalyst layer, and (iv) a second alkoxysilane-containingpolyolefin layer. These structures can be constructed by any one of anumber of different methods. For example, in one method the structure issimply built layer upon layer, e.g., the first alkoxysilane-containingpolyolefin layer is applied in any suitable manner to the glass,followed by the application of the catalyst layer to the firstalkoxysilane-containing polyolefin layer, followed by the application ofthe second alkoxysilane-containing polyolefin layer to the catalystlayer. The application of the catalyst layer to the firstalkoxysilane-containing polyolefin and the application of the secondalkoxysilane-containing polyolefin to the catalyst layer can be by anyprocess known in the art, e.g., extrusion, calendering, solution castingor injection molding. In another method, the first and secondalkoxysilane-containing polyolefin layers and catalyst layer are formedinto a multi-layer structure which is then applied to the glass layer.

The polymeric materials used in the practice of this invention, i.e.,the first and second alkoxysilane-containing polyolefin layers, can beused to construct electronic device modules, e.g., photovoltaic or solarcells, in the same manner and using the same amounts as the encapsulantmaterials known in the art, e.g., such as those taught in U.S. Pat. No.6,586,271, US Patent Application Publication US2001/0045229 A1, WO99/05206 and WO 99/04971. These materials can be used as “skins” for theelectronic device, i.e., applied to one or both face surfaces of thedevice, or as an encapsulant in which the device is totally enclosedwithin the material. Typically, the polymeric materials are applied tothe device by the layer upon layer technique described above butalternatively, a multi-layer laminated structure comprising the catalystlayer sandwiched between the first and second alkoxysilane-containingpolyolefin layers can first be prepared and then applied first to oneface surface of the device, and then to the other face surface of thedevice followed by the application of a glass cover to one or bothsurfaces of the multi-layer laminated structures now in adherence to theelectronic device.

In another embodiment, the polymeric materials used in the practice ofthis invention can be used to construct safety glass in the same manneras that known in the art. In this application, typically a multi-layerlaminated structure comprising the catalyst layer sandwiched between thefirst and second alkoxysilane-containing polyolefin layers is firstprepared and laminated to one sheet of glass. This is followed bylaminating a second sheet of glass to the open facial surface of themulti-layer laminated structure, i.e., the polymeric film.Alternatively, the polymeric film can be built layer by layer upon oneof the facial surfaces of the first glass layer.

Other applications in which the method of this invention is usefulinclude as a sealant for insulated glass, as a coating for glass (e.g.,to provide a visible or UV-light shield), and as a general adhesive forglass.

The following examples further illustrate the invention. Unlessotherwise indicated, all parts and percentages are by weight.

SPECIFIC EMBODIMENTS Comparative Examples 1 and 2

ENGAGE® 8100 resin (available from The Dow Chemical Company) is anethylene-octene copolymer with a density of 0.87 g/cm³ and a melt indexof 1 (measured according to ASTM D1238). The resin is mixed with 100 ppmof IRGANOX 1076® antioxidant (octadecyl3,5-di-(tert)-butyl-4-hydroxyhydrocinnamate)) available from CibaSpecialties Chemicals Corporation, and several other additivesidentified in Table 1.

TABLE 1 Polyolefin Formulation Comparative Comparative Component Example1 Example 2 ENGAGE 8100 97.22 97.34 CYASORB UV 531 0.3 0.3 CHIMASSORB944 LD 0.1 0.1 TINUVIN 622 LD 0.1 0.1 WESTON 399 0.2 0.08 Silane (DowCorning Z- 2 2 6300) LUPEROX-101 0.08 0.08 Catalyst (DBTDL) 0 0.06 Total100 100

CYASORB UV 531 is a light absorber (2-hydroxy-4-n-octoxybenzophenone)available form Cytec Industries Inc.

CHIMASSORB 944 LD is an oligomeric hindered amine light stabilizer(poly[[6-[1,1,3,3-tetramethylbutyl)amino]-s-triazine-2,4-diyl]-[(2,2,6,6-tetramethyl-4-piperidyl)imino]-hexamethylene-[(2,2,6,6-tetramethyl-4-piperidyl)imino]])available from Ciba Specialty Chemicals Corporation.

TINUVIN 622 LD is also a hindered amine light stabilizer (butanedioicacid, dimethylester-4-hydroxy-2,2,6,6-tetramethyl-piperidine ethanol)available from Ciba Specialty Chemicals Corporation.

WESTON 399 is a heat stabilizer (trisnonyiphenyl phosphite) availablefrom Chemtura Corporation.

DOW CORNING Z-6300 is a coupling agent (vinyltrimethoxysilane) availablefrom the Dow Corning Corporation.

LUPEROX-101 is polymerization initiator (a mixture of2,5-dimethyl-2,5-di(t-butylperoxy)hexane (60-100 wt %),3,3,6,6-tetramethyl-1,2-dioxacyclohexane (3-7 wt %), and di-tert-butylperoxide (0.1-1 wt %) available from Arkema Canada Inc.

DBTDL is dibutyltin dilaurate, an organotin used as a polymerizationcatalyst.

ENGAGE® 8100 pellets are dried at 40° C. overnight in a dryer. Thepellets and the additives are then dry mixed and placed in a drum andtumbled for 30 minutes. The silane and peroxide are then poured into thedrum and all are tumbled for another 15 minutes. The well mixedmaterials are then fed to a film extruder for film casting. Film is caston a film line (Killion Single Screw Extruder, 24 inches sheet die). Theprocessing conditions are summarized in Table 2.

TABLE 2 Processing Conditions Temperature (° C.) Ext. RPM Amp Head P(psi) Zone 1 Zone 2 Zone 3 Ad. Die Ad. Die 25 22 2,940 148.9 162.8 176.7176.7 182 127/140/126

A 18-19 mil thickness film is saved at 5.3 ft/min. The film sample issealed in an aluminum bag to avoid UV irradiation and absorption ofmoisture. The adhesion to glass and material strength at hightemperature (85° C.) are tested and the results are reported below.

The method used for the adhesion test is the 180° peel test. The testsample is prepared by placing the film on the top of glass underpressure in a compression molding machine. The desired adhesion width is1.0 in. A Teflon sheet is placed between the glass and the material toseparate the glass and polymer for the purpose of test setup. Theconditions for the glass/film sample preparation are:

-   -   1) 160° C. for 3 min at 2000 lbs    -   2) 160° C. for 30 min at 8000 lbs    -   3) Cool to room temperature at 8000 lbs.    -   4) Remove the sample from the chase and allow 48 hours for the        material to condition at room temperature before the adhesion        test.

The adhesion strength is measured with a materials testing system(Instron 5581). The loading rate is 2 in/min and the tests are run atambient conditions (24° C. and 50% RH). A stable peel region is needed(about 2 inches) to evaluate the adhesion to glass. The ratio of peelload in the stable peel region over the film width is reported as theadhesion strength. The results are reported in Table 3.

TABLE 3 Test Results of Adhesion to Glass Conditions for Adhesionmolding on Strength glass (N/mm) Comp. Example 1 160° C., one hour 10Comp. Example 2 160° C., one hour 0.1

The material strength (tensile) at high temperature is tested accordingto ASTM D638 using a dog bone sample at 85 C. The loading rate is 2in/min. The Comparative Example 1 could not be tested at 85 C becausethe film is too soft at this temperature to be gripped. The tensilestrength (maximum stress) of the Comparative Example 2 at 85 C is 0.3MPa. Comparative Example 1 shows that film extruded without catalystadheres to glass but does not have sufficient tensile strength.Comparative Example 2 shows that film extruded with catalyst hassufficient tensile strength, but it does not adhere to glass.

Example of the Invention

ENGAGES 8200 resin (available from The Dow Chemical Company) is anethylene-octene copolymer with a density of 0.87 g/cm³ and a melt indexof 5 (measured according to ASTM D1238). It is grafted with VTMS andcast to film in a Killion Single Screw Extruder under conditions similarto those described above. Five layers of the VTMS-grafted polyolefinfilm, which weighs a total of 8 grams, are placed on a sheet of glass asshown in FIG. 1. Varying amounts of catalyst (Ken-React NZ01 which isneopentyl(diallyloxy)zirconium trineodecanoate produced commercially byKenrich Petrochemicals) are applied between layers 4 and 5 using asyringe as shown in FIG. 4. The highest level of catalyst, 20,000 ppm,is applied neat, and the lower concentrations of catalyst are applied as0.5 mL solutions dissolved in ethyl acetate.

TABLE 4 Amounts of Catalyst Added to Multi-Layer Structure Sample Number1 2 3 4 5 Amount of Catalyst 160 16 8 4 0.8 Used (mg) CatalystConcentration 20,000 2,000 1,000 500 100 in Finished Structure (ppm)*Catalyst concentration was calculated by dividing the mass of thecatalyst by the mass of the polymer film.

Adhering film to glass is achieved through compression molding by usinga heated Carver press. A Teflon sheet carved in the middle and a metalchase are placed on top of the cleaned glass followed by the five layersof film, including the catalyst between layers 4 and 5. The scheme ofthe architecture is shown in FIG. 2. The compression molding procedureis as follows:

-   -   1. 150° C. for 3 minutes at 3,000 lb;    -   2. 150° C. for 7 minutes at 8,000 lb; and    -   3. Cool to room temperature at ambient conditions.

Adhesion testing is run by using an Instron machine with the loadingrate of 2 in/min at ambient conditions (24° C. and 50% RH). The ratio ofpeel load over the film width (N/mm) is reported as the adhesionstrength and the test is stopped after a stable peel region is observed.The test results are shown in FIG. 3. The adhesion to glass is lost withthe concentrated catalyst at 20,000 ppm, but improved when the catalystconcentration decreased to 2000 ppm. It is further improved when thediluted catalyst concentration is below 1000 ppm.

Dynamic Mechanical Testing Analysis (DMTA) is run by using an ARES withthe frequency of 10 rad/sec and strain of 0.1% to measure thevisco-elastic properties of samples in the solid state as a function oftemperature from −100° C. to 200° C. The sample without catalyst isadded as the control and two samples with different catalystconcentration are tested as a comparison. Cured ethylene vinyl acetate(EVA) is tested as a benchmark. The results are shown in FIG. 4.

The storage modulus of the control sample drops above 70° C. and themeasurement cannot be performed due to the thermal deformation of thesample. The benchmark EVA, cured at 160° C. for 30 minutes to a gelcontent of 89.7% as measured by ASTM D2765, exhibited a storage modulusplateau at temperatures above 70° C. The two VTMS-g-EG8200 samples withcatalyst show a behavior similar to that of the cured EVA. Thecrosslinking of these two samples is carried out in water at 65° C.overnight and 90° C. for one day. Their gel contents are comparable−65.8% for the 1000 ppm sample and 63.7% for the other sample. Combinedwith the results of the adhesion test, 1000 ppm of catalyst arepreferred for the silane crosslinked EG8200 to achieve both thermal andmechanical properties and adhesion to glass.

Although the invention has been described in considerable detail throughthe preceding description, drawings and examples, this detail is for thepurpose of illustration. One skilled in the art can make many variationsand modifications without departing from the spirit and scope of theinvention as described in the appended claims. All United States patentsand published or allowed United States patent applications referencedabove are incorporated herein by reference.

1. A method of making a laminated structure, the structure comprising(i) a glass layer, (ii) a first alkoxysilane-containing polyolefin (PO)layer, (iii) a catalyst layer, and (iv) a second alkoxysilane-containingpolyolefin layer, each layer having opposing facial surfaces, the methodcomprising the steps of applying in adhering contact: A. One facialsurface of the first PO layer to one facial surface of the glass layer;B. The catalyst layer to the facial surface of the first PO layeropposite the facial surface of the first PO layer in adhering contactwith the glass layer; and C. The second PO layer to the facial surfaceof the catalyst layer opposite the facial surface of the catalyst layerin adhering contact with the first PO layer.
 2. The method of claim 1 inwhich the catalyst layer is applied by painting, spraying or wiping acomposition comprising the catalyst onto one facial surface of the firstPO layer.
 3. The method of claim 1 in which the catalyst layer is a filmcomprising a catalyst homogeneously distributed within the film.
 4. Themethod of claim 3 in which the first and second PO layers comprise apolyolefin grafted with an alkoxysilane group, and the film of thecatalyst layer comprises the same polyolefin as that in the first andsecond PO layers except without the alkoxysilane groups.
 5. The methodof claim 3 in which at least one of the first and second PO layerscomprises a silane copolymer.
 6. A laminated structure comprising (i) aglass layer, (ii) a first alkoxysilane-containing polyolefin (PO) layer,(iii) a catalyst layer, and (iv) a second alkoxysilane-containingpolyolefin layer, each layer having opposing facial surfaces and: A. Onefacial surface of the first PO layer in adhering contact with one facialsurface of the glass layer; B. One facial surface of the catalyst layerin adhering contact with the facial surface of the first PO layeropposite the facial surface of the first PO layer in adhering contactwith the glass layer; and C. One facial surface of the second PO layerin adhering contact with the facial surface of the catalyst layeropposite the facial surface of the catalyst layer in adhering contactwith the first PO layer.
 7. The laminated structure of claim 6 in whichthe first and second PO layers comprise a polyolefin grafted with analkoxysilane group, and each comprises an ethylene/α-olefin copolymerthat has before grafting a density less than 0.91 g/cm³ and a melt indexless than 75 g/10 min.
 8. The laminated structure of claim 6 in whichthe catalyst layer also comprises an ethylene/α-olefin copolymer thathas before grafting a density less than 0.91 g/cm³ and a melt index lessthan 75 g/10 min.
 9. The laminated structure of claim 6 in which thecatalyst layer comprises a Lewis or Bronsted acid or base.
 10. Thelaminated structure of claim 6 in the form of a PV panel, solar cell,safety glass or insulated glass.